This invention relates to a method of recording on a magnetooptical disc which allows recording, reproduction and erase.
Currently, optical discs of read-only type are nearly in the stage of being practically applicable and those of add-on type are becoming available commercially. All these optical discs have large capacities and non-contact characteristics and they are easy to exchange. Magnetooptical discs have all these advantageous characteristics and have the additional advantage that data can be rewritten easily. Thus, they can be used not only where optical discs could be used before but potentially also where floppy discs and magnetic discs have been employed. When a magnetooptical disc is used as a code data memory, however, it used to be considered a problem that data could not be rewritten (overwrite) as easily as on a floppy disc or a magnetic disc. For this reason, a common practice has been, when it is desired to enter new data where old data already exists, to erase (initialize) the area first and then to write new data. This means that it takes twice as long in time as if use is made of a device with overwrite capability. Although it has been known, as an overwrite method on a magnetooptical disc, to modulate the magnetic write field while keeping the incident laser power constant on the recording medium, the inductance of the coil for generating the magnetic field tends to become too large by this method and since high-speed modulation of the magnetic field is difficult, the speed of data transmission becomes limited.